This invention concerns a method of induction-heat melting treatment of powders and a device for this method, and to be more specific, concerns a method of induction-heat melting treatment of powders and a device for this method by which metals, contained in incineration ash, fly ash, and other forms of ash treated as general waste, can be recovered at high purity and high recovery and by which the incineration ash, fly ash, etc. can be rendered harmless.
Combustibles that have been separated from among industrial waste and domestic waste are incinerated in an incinerator after collection and subject to dumping, landfill treatment, etc. in the form of incineration ash. Meanwhile, when such wastes are combusted, they become so-called fly ash upon vaporization of various low-boiling-point components. Since this fly ash contains large amounts of metals, such as lead, cadmium, chromium, zinc, arsenic, mercury, etc., in comparison to the abovementioned incineration ash, it is collected by means of a bag filter, etc. equipped with slaked lime, etc. and thereby prevented from becoming dispersed into the external environment as exhaust combustion gas.
Since the fly ash that has thus been collected contains large amounts of metals as has been mentioned above, it not only cannot be subject to landfill disposal directly as general waste but also requires strict control in terms of environmental sanitation. Fly ash is thus subject to treatment, such as adjustment of the pH to 11 to 14, for making the metals insoluble in water and thereby preventing elution of the metals, and subsequent mixing with concrete and dumping at a disposal site as concrete-sealed matter.
However, large amounts of unreacted slake lime remain in fly ash, and when the pH of fly ash becomes high, lead and zinc, which are the amphoteric metals among the metals contained in fly ash, become more readily eluted in water. This has thus been a problem especially for landfill disposal.
Thus presently in order to prevent elution and render the fly ash harmless, fly ash is treated with organic chelates or inorganic chemicals, etc., which make use of crystallization reactions. However, such treatment methods have the following problems.
(1) Organic chelate products are decomposed by soil microbes, resulting in the elution of zinc and lead.
(2) Organic treatment products are dissolved by the humic acid in the soil, resulting in the elution of zinc and lead.
(3) Though products of treatment by inorganic chemicals are excellent in long term stability, the amount of treatment product increases, thus resulting in the shortening of the lifetimes of landfill disposal sites.
Also, since metals that have been sealed in concrete become readily eluted when the pH is lowered by acid rain, etc., methods for removing metals without fail from within fly ash have been demanded.
On the other hand, ash melting methods have been noted by various municipalities not only in terms of volume-reduction effects but also in that large merits are provided in terms of enabling the ash to be rendered into harmless matter with which there is no elution of metals, etc. and improving the recycling rate. However, ash melting furnaces, such as plasma melting furnaces, reverberatory melting furnaces, electric resistance melting furnaces, etc., which can be erected adjacent existing incineration furnaces, are all high in construction cost and running cost, etc. and this has been an impeding factor in the introduction and spreading of ash melting methods among municipalities.
As an example of application of an induction-heat melting treatment device to the melting of the abovementioned incineration ash and fly ash, the device of FIG. 8 has been proposed. As shown in FIG. 8, this induction-heat melting treatment device 100 is comprised of a ceramic shell part 102a of a large diameter (approximately 2 meters) and a ceramic lower part 102b, formed to have the shape of an inverted cone, and is equipped with a hopper 102, which is connected to a powder supplying pipe 101 at the upper end, and an induction heating coil 103, which surrounds the outer periphery of the cylindrical shell part 102a of the abovementioned hopper 102. The melt resulting from the melting of ash inside the abovementioned hopper 102 is supplied to a melt storage tank 105 via a conical liquid distributor 104, provided at the exit at the lower end of the abovementioned hopper.
However, the above-described induction-heat melting treatment device 100 shown in FIG. 8 had the following problems.
(1) Due to the poor heat conduction of ash, a large amount of time is required for all of the ash stored in the large-diameter hopper 102 to melt. The amount treated per unit time was thus low, the thermal efficiency was also low, and as a result, the running cost was high.
(2) Since the interiors of hopper 102 and melt storage tank 105 are at atmospheric pressure and since the area for vaporization of the metals in the melt after the melting of ash is not large, it was difficult to render the ash slag completely harmless by vaporization of the metals in the melt. The metals also could not be recovered at high purity and high recovery.
(3) Due to the poor heat conduction of ash, when attempts were made to increase the treatment rate of ash, hopper 102, etc. and other parts of the device had to be made large, leading to increased equipment cost.
An object of this invention is to provide a method of induction-heat melting treatment of powders and a device for this method, which solve the abovementioned problems of the prior art, enable the rendering of incineration ash, fly ash, and other ash harmless by favorable removal of the metals contained in the ash, enable the metals to be recovered at high purity and high recovery, are high in equipment productivity, and are low in running cost.
(First Aspect: Method of Induction-heat Melting Treatment)
The first aspect of this invention is a method of induction-heat melting treatment of metal-oxide-containing powders, which comprises
a process in which a metal-oxide-containing powder is stored in a closed hopper,
a process in which the abovementioned metal-oxide-containing powder that has been stored in the abovementioned closed hopper is supplied at a prescribed flow rate to an induction heating pipe, which is comprised of dielectric material and has been induction heated to or higher than a prescribed temperature, and the abovementioned metal-oxide-containing powder that falls through the abovementioned induction heating pipe is heated to be melted while at least a part of the metal oxides are reduced,
a process in which the melt that has been obtained by melting is heated while being stored in a receiving container, made of dielectric material, to reduce the remaining metal oxides,
a process in which the liquid-film-like melt flow that overflows and flows down from the abovementioned receiving container is exposed to a vacuum atmosphere to cause the metals in the melt to vaporize and thereby convey the metals along with the ascending evacuation flow,
a process in which the metal vapor particles and/or the condensed metal particles in the abovementioned ascending evacuation flow are collected by means of an electric precipitation means,
a process in which the melt flow that overflows and flows down from the abovementioned receiving container is received and stored in a melt storage tank, and
a process in which the metal that has been collected by and has accumulated on the abovementioned electrostatic precipitation means is removed and recovered from the abovementioned precipitation means, and
with which at least one of either the abovementioned induction heating pipe and the abovementioned receiving container is formed from carbon material or graphite material.
With this invention""s method of induction-heat melting treatment of powders arranged as described above, incineration ash, fly ash, or other metal-oxide-containing powder, which has been vacuum dried in advance, is dropped at a prescribed flow rate through an induction heating pipe, comprised of dielectric material. The induction heating pipe, comprised of carbon material, graphite material, or other dielectric material, is heated by an induction heating coil, and by the radiant heat of the induction heating pipe that has been heated to a high temperature, the metal-oxide-containing powder is heated indirectly and the metal-oxide-containing powder is thereby melted while being reduced at least in part. When the abovementioned carbon material or graphite material, both of which are dielectric materials, is used as the material of the induction heating pipe, the metal-oxide-containing powder will be melted favorably since the reduction of the metal-oxide-containing powder will be promoted and the metal oxides will tend to be converted into metals more readily in comparison to the case of vacuum reduction by resistive heating without the use of a reducing agent. The abovementioned prescribed temperature is a temperature at which at least part of the metal oxides will be reduced by carbon or carbon monoxide. The abovementioned prescribed flow rate is a flow rate that matches the rates of such heating, reduction, melting, etc. Since a powder is thus dropped through an induction heating pipe heated to a high temperature and heated, reduced, and melted by the radiant heat, the abovementioned powder, which is poor in heat conduction, can be heated and melted efficiently and the equipment productivity (heat melting treatment amount per unit time) can be made high.
Other materials that can be used as the material of the induction heating pipe include high-melting-point metals, such as molybdenum, which is a dielectric material, and dielectric ceramic material, etc., and the same heating, reduction, and melting effects can also be obtained by adding a reducing material, such as carbon material, etc., in the abovementioned metal-oxide-containing powder.
The melt resulting from the melting is stored in a receiving container comprised of a dielectric material, such as that mentioned above. The receiving container comprised of dielectric material is heated by an induction heating coil and the melt in the high-temperature receiving container is heated further by conductive heat transfer and convective heat transfer to a temperature at which the melt will maintain adequate fluidity.
Also, since the highly fluid melt is made to overflow and flow down from the receiving container in the form of a liquid film and this liquid film is exposed to a prescribed vacuum atmosphere, the metals in the melt can be vaporized efficiently and at high purity.
Furthermore, since the metal vapor is carried along with the ascending evacuation flow and the metal vapor particles and/or condensed metal particles in the ascending evacuation flow are collected by the electric precipitation means, the metals can be collected and accumulated extremely efficiently while being kept at high purity and without becoming contaminated whatsoever.
Since the metals that have accumulated to a prescribed amount in the electric precipitation means is taken out from the electric precipitation means and removed and recovered from the electric precipitation means for example by heating and melting, metals of high purity can be recovered at high recovery. The electric precipitation means, which is regenerated upon recovery of the accumulated metals, is used repeatedly.
Meanwhile, the melt of the powder from which the metals have been vaporized and eliminated, is stored in the melt storage tank, and when the amount of stored melt reaches a prescribed amount, the melt is, for example, granulated by the water granulation method or treated as necessary by some other treatment method according to composition and use.
(First Aspect: Device for Induction-heat Melting Treatment)
This invention provides, as a first technical means for achieving the above-described object, a device for induction-heat melting treatment of metal-oxide-containing powders, the principal parts of which are comprised of
a closed hopper, which stores a metal-oxide-containing powder,
a heat-resistant piping, which is equipped with a means for controlling the flow rate of the abovementioned metal-oxide containing powder and supplies the abovementioned metal-oxide-containing powder from the abovementioned closed hopper to an induction heating pipe,
an induction heating pipe, which is comprised of dielectric material and the inner peripheral surface of the upper end part of which contacts the outer peripheral surface of the lower end part of the abovementioned heat-resistant piping in a manner enabling sliding in the vertical direction,
a raising/lowering drive mechanism, which holds the upper end part of the abovementioned induction heating pipe in a manner enabling raising and lowering,
a receiving container, which is made of dielectric material and surrounds the lower part of the abovementioned induction heating pipe and receives the melt of the powder, melted in the abovementioned induction heating pipe, while letting the melt overflow,
a cylindrical upper vacuum chamber, which encloses the lower part of the abovementioned heat-resistant piping, the abovementioned induction heating pipe, a part of the abovementioned raising/lowering mechanism, and the abovementioned receiving container, and is connected to an evacuation means,
an induction heating coil, which is disposed so as to externally surround the positions of the abovementioned cylindrical upper vacuum chamber corresponding to the abovementioned induction heating pipe,
an electric precipitation means, which is disposed above the abovementioned receiving container in the abovementioned cylindrical upper vacuum chamber so as to externally surround the abovementioned induction heating pipe and/or is disposed inside an evacuation pipe from the abovementioned cylindrical upper vacuum chamber and collects the metal vapor particles and/or the condensed metal particles resulting from vaporization from the liquid-film-like melt that overflows and flows down from the abovementioned receiving container,
a tilting pan, which receives the melt that overflows and flows down from the abovementioned receiving container and is supported in a manner enabling tilting and return to the horizontal position,
a tilting mechanism for the abovementioned tilting pan,
a melt storage tank, which receives and stores the melt from the abovementioned tilting pan, and.
a lower vacuum chamber, which encloses the abovementioned tilting pan and melt storage tank and is connected to the lower end of the abovementioned cylindrical upper vacuum chamber.
Since this invention""s device for induction-heat melting treatment of metal-oxide-containing powders is arranged in the above manner, it provides the same effects as the above-described method of induction-heat melting treatment of metal-oxide-containing powders by this invention.
As a second technical means, this invention""s device for induction-heat melting treatment of metal-oxide-containing powders according to the first aspect, equipped with the above-described first technical means, is preferably arranged so that
the abovementioned lower vacuum chamber is equipped with a partition plate, which divides the interior of the abovementioned lower vacuum chamber into an upper chamber that encloses the abovementioned tilting pan and a lower chamber that encloses the abovementioned melt storage tank,
a through hole, which is provided in the abovementioned partition plate in order to cause the melt to flow down from the abovementioned tilting pan to the abovementioned melt storage tank,
an opening/closing lid, which opens and closes the abovementioned through hole,
an atmospheric inlet pipe, which is connected to the abovementioned lower chamber and is equipped with an atmospheric inlet valve,
an evacuation pipe, which is connected to the abovementioned lower chamber, and
an opening/closing door, which is provided at the side wall of the abovementioned lower chamber for moving the abovementioned melt storage tank in and out of the lower chamber.
With the above arrangement, when a prescribed amount of melt has accumulated in the melt storage tank, the tilting pan is returned to the horizontal position, the through hole of the partition plate of the lower vacuum chamber is closed by the circular lid while the melt is stored in the tilting pan, and the interiors of the upper chamber and the cylindrical upper vacuum chamber are kept at vacuum to enable induction-heat melting treatment of the metal-oxide-containing powder to be continued.
Also, upon stopping the evacuation via the evacuation pipe of the lower chamber and opening the atmospheric inlet valve to introduce atmosphere into the lower chamber and thereby returning the interior of the lower chamber to atmospheric pressure, the opening/closing door can be opened to draw the melt storage tank out of the lower chamber and carry in a spare melt storage tank into the lower chamber.
Thereafter, the opening/closing door and the atmospheric inlet valve are closed and the interior of the lower chamber is evacuated via the evacuation pipe of the lower chamber to enable the degree of vacuum to be raised until the interior of the lower chamber will be at the same pressure as the interior of the upper chamber.
The circular lid is then opened and the tilting pan is tilted again to cause the melt to flow down into the melt storage tank and thereby begin storage again, and during the induction-heat melting treatment of the powder, evacuation is continued via the evacuation pipe at the upper end of the cylindrical upper vacuum chamber and the evacuation pipe 15 of the lower chamber to enable the interiors of the cylindrical upper vacuum chamber and the lower vacuum chamber to be kept at a prescribed degree of vacuum.
As a third technical means, this invention""s device according to the first aspect for induction-heat melting treatment of metal-oxide-containing powders that employs the above-described first technical means may be arranged so that
the abovementioned lower vacuum chamber is equipped with
a partition plate, which divides the interior of the abovementioned lower vacuum chamber into an upper chamber that encloses the abovementioned tilting pan and a lower chamber that encloses the abovementioned melt storage tank,
a partition wall, which partitions the abovementioned lower chamber into the two parts of left and right lower chambers,
left and right through holes, which are provided in the abovementioned partition plate in order to cause the melt to flow down from the abovementioned tilting pan to each of the melt storage tanks enclosed respectively in the abovementioned left and right lower chambers,
opening/closing lids, which open and close the abovementioned left and right through holes, respectively,
atmospheric inlet pipes, which are respectively equipped with atmospheric inlet valves and connected respectively to the abovementioned left and right lower chambers,
evacuation pipes, which are connected respectively to the abovementioned left and right lower chambers, and
opening/closing doors, which are provided at the side walls of the abovementioned left and right lower chambers, respectively, for enabling the abovementioned melt storage tanks to be moved in and out of the respective lower chambers.
With the above arrangement, when for example a prescribed amount of melt has accumulated in the melt storage tank inside the lower chamber at the right side, the tilting pan is returned once to the horizontal position, the opening/closing lid of the adjacently disposed left melt storage tank is opened while the melt is being stored in the tilting pan, and then the tilt of the tilting pan is switched so that the melt will flow into the left melt storage tank. The right melt storage tank is then cut off from the vacuum system by closing the through hole of the partition plate of the lower vacuum chamber by the circular lid so that the induction-heat melting treatment of the powder can be continued while keeping the interiors of the upper chamber and the cylindrical upper vacuum chamber at vacuum.
Also, upon stopping the evacuation via the evacuation pipe of the right lower chamber and opening the atmospheric inlet valve to introduce atmosphere into the lower chamber and returning the interior of the lower chamber to atmospheric pressure, the opening/closing door can be opened to enable the melt storage tank to be drawn outside the lower chamber and a spare melt storage tank to be carried into the lower chamber.
Subsequently, by closing the opening/closing door and the atmospheric inlet valve of the right lower chamber prior to accumulation of a prescribed amount of melt in the left melt storage tank and then evacuating the interior of the lower chamber via the evacuation pipe of the lower chamber, the degree of vacuum in the lower chamber can be increased until the pressure becomes equivalent to that of the interior of the upper chamber.
The circular lid is then opened, the tilting pan is tilted again towards the melt storage tank in the right lower chamber to start storage again, and during the induction-heat melting treatment of the powder, evacuation is continued via the evacuation pipe at the upper end of the cylindrical upper vacuum chamber and the evacuation pipe of the lower vacuum chamber to enable the interiors of the cylindrical upper vacuum chamber and the lower vacuum chamber to be maintained at a prescribed level.
By thus simply switching the tilt of the tilting pan in the direction of the melt storage tank in which the melt is to be stored, the induction-heat melting treatment of the powder and the drawing out of the melt to the exterior can be carried out in a continuous manner.
As a fourth technical means, this invention""s device according to the first aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described first to third technical means is preferably arranged with
the abovementioned induction heating pipe and the abovementioned receiving container being formed from carbon material, graphite material, or high-melting-point metal.
Since carbon materials and graphite materials are high in dielectric characteristics and electrical conductivity and are also strong against chemical erosion by the metal oxide melt, they are suitable as materials for the induction heating pipe and as materials for the receiving container. Also, these materials are favorable in that they maintain a reducing atmosphere inside the induction heating pipe and promote the action of reduction of the metal oxides. Furthermore, these materials are significantly economical in comparison to molybdenum and other high-melting-point metals.
Among high-melting-point metals, molybdenum is preferable. Since molybdenum is high in dielectric characteristics and conductivity, strong against chemical erosion by metal oxide melts, and is furthermore less likely than tungsten, etc. to undergo reaction with the carbon material used as the reducing agent, degradation of strength due to carburizing, or degradation of strength due to reaction with the iron in incineration ash, it is suitable as the material for the induction heating pipe and the material for the receiving container. Furthermore, molybdenum is high in high-temperature strength in comparison to carbon materials and graphite materials and, though having the problem of being expensive, is favorable as the material for the induction heating pipe and the material for the receiving container.
As a fifth technical means, this invention""s device according to the first aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described first to fourth technical means may be arranged with the abovementioned induction heating pipe and the abovementioned receiving container being formed from dielectric ceramic material.
Dielectric ceramic materials are favorable in that they are low in thermal expansion coefficient in comparison to carbon materials, graphite materials, and high-melting-point metals, can be readily connected to the heat-resistant piping for supplying the powder, and enable highly precise adjustment of the gap between the below-described protruding part, to be provided at the inner bottom surface part of the receiving container that is immediately below the induction heating pipe, and the lower end part of the induction heating pipe.
As a sixth technical means, this invention""s device according to the first aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described first to fifth technical means is preferably arranged with
a protruding part being equipped at the inner bottom surface part of the abovementioned receiving container that is immediately below the abovementioned induction heating pipe and the abovementioned raising/lowering drive mechanism being comprised of a servo motor.
With such an arrangement, the cross-sectional area of the gap, between the outer surface of the protruding part, provided at the inner bottom surface part of the abovementioned receiving container that is immediately below the abovementioned induction heating pipe, and the inner surface of the lower end part of the induction heating pipe or the edge of the inner surface of the lower end part of the induction heating pipe, can be adjusted at high precision by the raising and lowering movement of the induction heating pipe. As a result, the liquid-film-like melt that over flows and flows down from the receiving container can be made to overflow at a flow rate that is suited for the vaporization of metal upon exposure of the melt to vacuum. The rate of overflow of the melt is thus prevented from becoming so high that the rendering of the melt harmless will be made inadequate by the melt flowing into the lower melt storage tank without adequate vaporization of the metals in the melt. Also, since the rate of overflow will be prevented from becoming so small that the amount treated per unit time will become smaller than the capacity of the device, the equipment productivity of the device can be raised to the maximum.
As a seventh technical means, this invention""s device according to the first aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described first to sixth technical means is preferably arranged with the abovementioned receiving container being made to have an inverted trapezoidal cross-sectional shape and have grooves formed at suitable intervals along the circumference of the upper end thereof and/or being equipped, at the upper end of the side wall thereof, with a flange part that extends outward with grooves being formed at suitable intervals along the circumference of the abovementioned flange part.
With the above arrangement, the melt that overflows and flows down from the upper end of the side wall of the receiving container can be prevented from trailing along the outer surface of the side wall and can thus be made to form a liquid film that is separated from the outer surface of the side wall of the receiving container. As a result, the surface area of the liquid film that contacts the vacuum atmosphere will be approximately doubled, thus increasing the rate of vaporization of metal from the liquid-film-like melt and approximately doubling the amount treated per unit time.
Also, by providing grooves on the surface at which the liquid overflows from the upper end of the side wall of the receiving container and thereby varying the rate of overflow of liquid at each groove, openings are formed so that the metal vapor will not be trapped in the space between the liquid film, which falls like a waterfall from the upper end of the side wall of the receiving container, and the outer surface of the side wall of the receiving container and be prevented from escaping to the exterior.
In the case where there are no grooves, since the periphery of the receiving container will be covered entirely by the liquid film that falls like a waterfall from the abovementioned upper end of the side wall and the trapped metal vapor will not be able to escape to the exterior even when there is an ascending evacuation flow, the rate of vaporization of the metal will be small.
As an eighth technical means, this invention""s device according to the first aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described first to seventh technical means may be arranged with
notched parts being provided at suitable intervals along the circumference of the upper end of the side wall of the abovementioned receiving container.
With the above arrangement, the flow rate of the melt that flows outward from the notches will be increased in comparison to the case where there are no notches, provided that the flow rate of the melt that overflows and flows down from the upper end of the side wall of the receiving container is the same in both cases. The melt that overflows and flows down can thus be prevented from trailing along the outer surface of the side wall of the receiving container and can be made to form a liquid film that is separated from the outer surface of the side wall. As a result, the surface area by which the liquid film contacts the vacuum atmosphere is increased, thereby enabling the rate of vaporization of metal from the liquid-film-like melt to be made greater and the amount treated per unit time to be increased.
(Second Aspect: Method of Induction-heat Melting Treatment)
The second first aspect of this invention is a method of induction-heat melting treatment of metal-oxide-containing powders, which comprises
a process in which a metal-oxide-containing powder is stored in a closed hopper,
a process in which the abovementioned metal-oxide-containing powder that has been stored in the abovementioned closed hopper is supplied at a prescribed flow rate to an induction heating pipe, which is comprised of dielectric material and has been induction heated to or higher than a prescribed temperature, and the abovementioned metal-oxide-containing powder that falls through the abovementioned induction heating pipe is heated to be melted while at least a part of the metal oxides are reduced,
a process in which the melt that has been obtained by melting is heated while being stored in a packing, made of dielectric material, to reduce the remaining metal oxides,
a process in which the liquid-film-like melt flow that overflows and flows down from the abovementioned packing is exposed to a vacuum atmosphere to cause the metals in the melt to vaporize and thereby convey the metals along with the ascending evacuation flow,
a process in which the metal vapor particles and/or the condensed metal particles in the abovementioned ascending evacuation flow are collected by means of an electric precipitation means,
a process in which the melt flow that overflows and flows down from the abovementioned packing is received and stored in a melt storage tank, and
a process in which the metal that has been collected by and has accumulated on the abovementioned electrostatic precipitation means is removed and recovered from the abovementioned precipitation means, and with which at least one of either the abovementioned induction heating pipe and the abovementioned packing is formed from carbon material or graphite material.
With this invention""s method according to the second aspect of induction-heat melting treatment of powders arranged as described above, incineration ash, fly ash, or other metal-oxide-containing powder, which has been vacuum dried in advance, is dropped at a prescribed flow rate through an induction heating pipe, comprised of dielectric material. The induction heating pipe, comprised of carbon material, graphite material, or other dielectric material, is heated by an induction heating coil, and by the radiant heat of the induction heating pipe that has been heated to a high temperature, the metal-oxide-containing powder is heated indirectly and the metal-oxide-containing powder is thereby melted while being reduced at least in part. When the abovementioned carbon material or graphite material, both of which are dielectric materials, is used as the material of the induction heating pipe, the metal-oxide-containing powder will be melted favorably since the reduction of the metal-oxide-containing powder will be promoted and the metal oxides will tend to be converted into metals more readily in comparison to the case of vacuum reduction by resistive heating without the use of a reducing agent. The abovementioned prescribed temperature is a temperature at which at least part of the metal oxides will be reduced by carbon or carbon monoxide. The abovementioned prescribed flow rate is a flow rate that matches the rates of such heating, reduction, melting, etc. Since a powder is thus dropped through an induction heating pipe heated to a high temperature and heated, reduced, and melted by the radiant heat, the abovementioned powder, which is poor in heat conduction, can be heated and melted efficiently and the equipment productivity (heat melting treatment amount per unit time) can be made high.
Other materials that can be used as the material of the induction heating pipe include high-melting-point metals, such as molybdenum, which is a dielectric material, and dielectric ceramic material, etc., and the same heating, reduction, and melting effects can also be obtained by adding a reducing material, such as carbon material, etc., in the abovementioned metal-oxide-containing powder.
The melt resulting from the melting is stored in a packing comprised of a dielectric material, such as that mentioned above. The packing comprised of dielectric material is heated by an induction heating coil and the melt in the high-temperature packing is heated further by conductive heat transfer and convective heat transfer to a temperature at which the melt will maintain adequate fluidity.
Also, since the highly fluid melt is made to overflow and flow down from the packing in the form of a liquid film and this liquid film is exposed to a prescribed vacuum atmosphere, the metals in the melt can be vaporized efficiently and at high purity.
Furthermore, since the metal vapor is carried along with the ascending evacuation flow and the metal vapor particles and/or condensed metal particles in the ascending evacuation flow are collected by the electric precipitation means, the metals can be collected and accumulated extremely efficiently while being kept at high purity and without becoming contaminated whatsoever.
Since the metals that have accumulated to a prescribed amount in the electric precipitation means is taken out from the electric precipitation means and removed and recovered from the electric precipitation means for example by heating and melting, metals of high purity can be recovered at high recovery. The electric precipitation means, which is regenerated upon recovery of the accumulated metals, is used repeatedly.
Meanwhile, the melt of the powder from which the metals have been vaporized and eliminated, is stored in the melt storage tank, and when the amount of stored melt reaches a prescribed amount, the melt is, for example, granulated by the water granulation method or treated as necessary by some other treatment method according to composition and use.
(Second Aspect: Device for Induction-heat Melting Treatment)
This invention provides, as a second technical means according to the second aspect for achieving the above-described object, a device for induction-heat melting treatment of metal-oxide-containing powders, the principal parts of which are comprised of
a closed hopper, which stores a metal-oxide-containing powder,
a heat-resistant piping, which is equipped with a means for controlling the flow rate of the abovementioned metal-oxide containing powder and supplies the abovementioned metal-oxide-containing powder from the abovementioned closed hopper to an induction heating pipe,
an induction heating pipe, which is comprised of dielectric material and the inner peripheral surface of the upper end part of which contacts the outer peripheral surface of the lower end part of the abovementioned heat-resistant piping in a manner enabling sliding in the vertical direction,
a raising/lowering drive mechanism, which holds the upper end part of the abovementioned induction heating pipe in a manner enabling raising and lowering,
a packing, which is made of dielectric material and surrounds the lower part of the abovementioned induction heating pipe and receives the melt of the powder, melted in the abovementioned induction heating pipe, while letting the melt overflow,
a cylindrical upper vacuum chamber, which encloses the lower part of the abovementioned heat-resistant piping, the abovementioned induction heating pipe, a part of the abovementioned raising/lowering mechanism, and the abovementioned packing, and is connected to an evacuation means,
an induction heating coil, which is disposed so as to externally surround the positions of the abovementioned cylindrical upper vacuum chamber corresponding to the abovementioned induction heating pipe,
an electric precipitation means, which is disposed above the abovementioned packing in the abovementioned cylindrical upper vacuum chamber so as to externally surround the abovementioned induction heating pipe and/or is disposed inside an evacuation pipe from the abovementioned cylindrical upper vacuum chamber and collects the metal vapor particles and/or the condensed metal particles resulting from vaporization from the liquid-film-like melt that overflows and flows down from the abovementioned packing,
a tilting pan, which receives the melt that overflows and flows down from the abovementioned packing and is supported in a manner enabling tilting and return to the horizontal position,
a tilting mechanism for the abovementioned tilting pan,
a melt storage tank, which receives and stores the melt from the abovementioned tilting pan, and
a lower vacuum chamber, which encloses the abovementioned tilting pan and melt storage tank and is connected to the lower end of the abovementioned cylindrical upper vacuum chamber.
Since this invention""s device for induction-heat melting treatment of metal-oxide-containing powders is arranged in the above manner, it provides the same effects as the above-described method of induction-heat melting treatment of metal-oxide-containing powders by this invention.
As a second technical means, this invention""s device for induction-heat melting treatment of metal-oxide-containing powders according to the second aspect, equipped with the above-described second technical means, is preferably arranged so that
the abovementioned lower vacuum chamber is equipped with a partition plate, which divides the interior of the abovementioned lower vacuum chamber into an upper chamber that encloses the abovementioned tilting pan and a lower chamber that encloses the abovementioned melt storage tank,
a through hole, which is provided in the abovementioned partition plate in order to cause the melt to flow down from the abovementioned tilting pan to the abovementioned melt storage tank,
an opening/closing lid, which opens and closes the abovementioned through hole,
an atmospheric inlet pipe, which is connected to the abovementioned lower chamber and is equipped with an atmospheric inlet valve,
an evacuation pipe, which is connected to the abovementioned lower chamber, and
an opening/closing door, which is provided at the side wall of the abovementioned lower chamber for moving the abovementioned melt storage tank in and out of the lower chamber.
With the above arrangement, when a prescribed amount of melt has accumulated in the melt storage tank, the tilting pan is returned to the horizontal position, the through hole of the partition plate of the lower vacuum chamber is closed by the circular lid while the melt is stored in the tilting pan, and the interiors of the upper chamber and the cylindrical upper vacuum chamber are kept at vacuum to enable induction-heat melting treatment of the metal-oxide-containing powder to be continued.
Also, upon stopping the evacuation via the evacuation pipe of the lower chamber and opening the atmospheric inlet valve to introduce atmosphere into the lower chamber and thereby returning the interior of the lower chamber to atmospheric pressure, the opening/closing door can be opened to draw the melt storage tank out of the lower chamber and carry in a spare melt storage tank into the lower chamber.
Thereafter, the opening/closing door and the atmospheric inlet valve are closed and the interior of the lower chamber is evacuated via the evacuation pipe of the lower chamber to enable the degree of vacuum to be raised until the interior of the lower chamber will be at the same pressure as the interior of the upper chamber.
The circular lid is then opened and the tilting pan is tilted again to cause the melt to flow down into the melt storage tank and thereby begin storage again, and during the induction-heat melting treatment of the powder, evacuation is continued via the evacuation pipe at the upper end of the cylindrical upper vacuum chamber and the evacuation pipe 15 of the lower chamber to enable the interiors of the cylindrical upper vacuum chamber and the lower vacuum chamber to be kept at a prescribed degree of vacuum.
As a third technical means, this invention""s device according to the second aspect for induction-heat melting treatment of metal-oxide-containing powders that employs the above-described second technical means may be arranged so that
the abovementioned lower vacuum chamber is equipped with
a partition plate, which divides the interior of the abovementioned lower vacuum chamber into an upper chamber that encloses the abovementioned tilting pan and a lower chamber that encloses the abovementioned melt storage tank,
a partition wall, which partitions the abovementioned lower chamber into the two parts of left and right lower chambers,
left and right through holes, which are provided in the abovementioned partition plate in order to cause the melt to flow down from the abovementioned tilting pan to each of the melt storage tanks enclosed respectively in the abovementioned left and right lower chambers,
opening/closing lids, which open and close the abovementioned left and right through holes, respectively,
atmospheric inlet pipes, which are respectively equipped with atmospheric inlet valves and connected respectively to the abovementioned. left and right lower chambers,
evacuation pipes, which are connected respectively to the abovementioned left and right lower chambers, and
opening/closing doors, which are provided at the side walls of the abovementioned left and right lower chambers, respectively, for enabling the abovementioned melt storage tanks to be moved in and out of the respective lower chambers.
With the above arrangement, when for example a prescribed amount of melt has accumulated in the melt storage tank inside the lower chamber at the right side, the tilting pan is returned once to the horizontal position, the opening/closing lid of the adjacently disposed left melt storage tank is opened while the melt is being stored in the tilting pan, and then the tilt of the tilting pan is switched so that the melt will flow into the left melt storage tank. The right melt storage tank is then cut off from the vacuum system by closing the through hole of the partition plate of the lower vacuum chamber by the circular lid so that the induction-heat melting treatment of the powder can be continued while keeping the interiors of the upper chamber and the cylindrical upper vacuum chamber at vacuum.
Also, upon stopping the evacuation via the evacuation pipe of the right lower chamber and opening the atmospheric inlet valve to introduce atmosphere into the lower chamber and returning the interior of the lower chamber to atmospheric pressure, the opening/closing door can be opened to enable the melt storage tank to be drawn outside the lower chamber and a spare melt storage tank to be carried into the lower chamber.
Subsequently, by closing the opening/closing door and the atmospheric inlet valve of the right lower chamber prior to accumulation of a prescribed amount of melt in the left melt storage tank and then evacuating the interior of the lower chamber via the evacuation pipe of the lower chamber, the degree of vacuum in the lower chamber can be increased until the pressure becomes equivalent to that of the interior of the upper chamber.
The circular lid is then opened, the tilting pan is tilted again towards the melt storage tank in the right lower chamber to start storage again, and during the induction-heat melting treatment of the powder, evacuation is continued via the evacuation pipe at the upper end of the cylindrical upper vacuum chamber and the evacuation pipe of the lower vacuum chamber to enable the interiors of the cylindrical upper vacuum chamber and the lower vacuum chamber to be maintained at a prescribed level.
By thus simply switching the tilt of the tilting pan in the direction of the melt storage tank in which the melt is to be stored, the induction-heat melting treatment of the powder and the drawing out of the melt to the exterior can be carried out in a continuous manner.
As a fourth technical means, this invention""s device according to the second aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described second to third technical means is preferably arranged with
the abovementioned induction heating pipe and the abovementioned packing being formed from carbon material, graphite material, or high-melting-point metal.
Since carbon materials and graphite materials are high in dielectric characteristics and electrical conductivity and are also strong against chemical erosion by the metal oxide melt, they are suitable as materials for the induction heating pipe and as materials for the packing. Also, these materials are favorable in that they maintain a reducing atmosphere inside the induction heating pipe and promote the action of reduction of the metal oxides. Furthermore, these materials are significantly economical in comparison to molybdenum and other high-melting-point metals.
Among high-melting-point metals, molybdenum is preferable. Since molybdenum is high in dielectric characteristics and conductivity, strong against chemical erosion by metal oxide melts, and is furthermore less likely than tungsten, etc. to undergo reaction with the carbon material used as the reducing agent, degradation of strength due to carburizing, or degradation of strength due to reaction with the iron in incineration ash, it is suitable as the material for the induction heating pipe and the material for the packing. Furthermore, molybdenum is high in high-temperature strength in comparison to carbon materials and graphite materials and, though having the problem of being expensive, is favorable as the material for the induction heating pipe and the material for the packing.
As a fifth technical means, this invention""s device according to the second aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described second to fourth technical means may be arranged with the abovementioned induction heating pipe and the abovementioned packing being formed from dielectric ceramic material.
Dielectric ceramic materials are favorable in that they are low in thermal expansion coefficient in comparison to carbon materials, graphite materials, and high-melting-point metals, can be readily connected to the heat-resistant piping for supplying the powder, and enable highly precise adjustment of the gap between the below-described protruding part, to be provided at the inner bottom surface part of the packing that is immediately below the induction heating pipe, and the lower end part of the induction heating pipe.
As a sixth technical means, this invention""s device according to the second aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described second to fifth technical means is preferably arranged with
the abovementioned raising/lowering drive mechanism being comprised of a servo motor.
With such an arrangement, the cross-sectional area of the gap, between the outer surface of the protruding part, provided at the center of abovementioned packing that is immediately below the abovementioned induction heating pipe, and the inner surface of the lower end part of the induction heating pipe or the edge of the inner surface of the lower end part of the induction heating pipe, can be adjusted at high precision by the raising and lowering movement of the induction heating pipe. As a result, the liquid-film-like melt that overflows and flows down from the packing can be made to overflow at a flow rate that is suited for the vaporization of metal upon exposure of the melt to vacuum. The rate of overflow of the melt is thus prevented from becoming so high that the rendering of the melt harmless will be made inadequate by the melt flowing into the lower melt storage tank without adequate vaporization of the metals in the melt. Also, since the rate of overflow will be prevented from becoming so small that the amount treated per unit time will become smaller than the capacity of the device, the equipment productivity of the device can be raised to the maximum.
As a seventh technical means, this invention""s device according to the second aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described second to sixth technical means is preferably arranged with
the abovementioned packing composed of a protruding part at the center thereof, with a plurality of circular or semicircular pores around the outer circumference thereof and
a circular plate having a circular pore at the center thereof, and a downward slope from the outer circumference to the center pore, placed via a gap, and the abovementioned packing being in contact with the lower inner wall of said cylindrical upper vacuum chamber.
With such an arrangement, the cross-sectional area of the gap, between the outer surface of the protruding part, provided at the center of abovementioned packing that is immediately below the abovementioned induction heating pipe, and the inner surface of the lower end part of the induction heating pipe or the edge of the inner surface of the lower end part of the induction heating pipe, can be adjusted at high precision by the raising and lowering movement of the induction heating pipe via the servo motor. As a result, the liquid-film-like melt that overflows and flows down from the packing can be made to overflow at a flow rate that is suited for the vaporization of metal upon exposure of the melt to vacuum. The rate of overflow of the melt is thus prevented from becoming so high that the rendering of the melt harmless will be made inadequate by the melt flowing into the lower melt storage tank without adequate vaporization of the metals in the melt. Also, since the rate of overflow will be prevented from becoming so small that the amount treated per unit time will become smaller than the capacity of the device, the equipment productivity of the device can be raised to the maximum.
During the course of the liquid flowing on the slope of the packing, liquid-film can be produced. As a result, the surface area of the liquid film in contact with the vacuum atmosphere becomes large, making it possible to accelerate the vaporization of the metal from the melt, leading to a larger treating amount per unit period.
Also, by providing gaps between the cap and plate, the passage of the liquid flowing through the packing becomes better.
Since all of the melt supplied flows on the slope of the packing in a liquid-film like state, the surface area of the melt with the vacuum atmosphere does not become small like the case of utilizing the receiving container.
In the case of receiving the melt by the receiving container, the surface area of the liquid per unit volume becomes small and, thus, the metal vapor becomes difficult to be discharged out, resulting in low vaporization rate of the metal.
As an eighth technical means, this invention""s device according to the second aspect for induction-heat melting treatment of metal-oxide-containing powders that employs any of the above-described first to seventh technical means may be arranged with packing composed of an uneven packing material in which when the typical diameter is taken as the same as the sphere, the circumference ratio relative to the cross-section of the material is longer than the sphere, and a packing support, and the abovementioned packing being supported on the lower inner wall of said cylindrical upper vacuum chamber via the packing support.
With the above arrangement, by passing the melt through the packing layer supported on the lower inner wall of said cylindrical upper vacuum chamber via the packing support having the packing material in which when the typical diameter is taken as the same as the sphere, the circumference ratio relative to the cross-section of the material is longer than the sphere packed therein, the liquid-film can be formed on the surface of the packing material. By shaping the packing material into an uneven form, the pressure loss during the course of the melt flowing on the packing can be reduced. As a result, the surface area of the liquid-film in contact with the vacuum atmosphere can be increased, making it possible to accelerate the vaporization of the metal from the melt, leading to a larger treating amount per unit period.